Literature References: Natural filixic acid from male fern, Dryopteris filix-mas, is a mixture of six homologues, the 3 main components (BBB, PBB, PBP) of which are obtained by recrystallization from ethyl acetate. When raw filixic acid is purified by treatments with methanol but without recrystns from ethyl acetate, a product is obtained which seems to contain 3 additional homologues with an analogous composition but with acetyl groups in the side chain. Isoln: Luck, Ann.54, 119 (1845); Boehm, ibid.318, 253 (1901). Structure studies: Riedl, Ann.585, 32 (1954); Chan, Hassal, Experientia13, 349 (1957). Structure of the three main filixic acids: Penttilä, Sundman, Acta Chem. Scand.17, 191 (1963).